1. Field of the Invention
This invention relates to digital image processing through hardware using a so-called cubic convolution interpolation technique.
2. Description of the Prior Art
Digital image processing, the manipulation of images by computer, is a relatively recent development. In its short history, it has been applied to a variety of technical fields involving space, medical and color printing technologies, etc., with varying degrees of success.
In connection with space technology, for example, remote sensing data transmitted from unmanned satellites inherently involves geometric distortions (for example) and hence is required to undergo digital image compensation processing in order to obtain desired images. The digital image processing involves conversion of coordinate's axes of two-dimensional digital data, image enlargement, decompression, etc.
The coordinate conversion of the two-dimensional digital data is known as "resampling". In order to resample the digital input data, data processing techniques such as nearest neighbor interpolation, bilinear interpolation, and interpolation using the cubic convolution method are known.
The nearest neighbor interpolation is the simplest interpolation scheme, wherein the data of the output pixel (picture element) is taken to be that of the input pixel nearest to the position to which it maps. This interpolation however encounters a problem that introduces a sawtooth effect at the edges of the obtained image. On the other hand, bilinear interpolation obtains the output pixel by interpolating adjacent four-pixel neighborhoods, but still does not provide sufficient smoothing in contours. This problem is particularly notable if the geometric operation involves magnification.
The cubic convolution method, which will be described in detail hereinlater, is free from the problems of the above two interpolation techniques. The cubic convolution method involves executions of complex equations and is currently implemented by software, resulting in a large amount of wasteful time and the requirement of large capacity host computer.